1. Field of the Invention
The present invention is directed to the field of DC and low frequency AC current measuring by sensing the intensity of the resultant magnetic field produced by the flow of current in a conductive path.
2. Description of the Prior Art
Non-contacting current measuring instruments have been developed in the past which utilize complex sensing pickups with several cores and several windings for excitation sensing and feedback.
U.S. Pat. No. 3,801,907 illustrates a direct current measuring device utilizing two pair of cores with multiple control windings, bias windings and feedback windings to perform measurements with saturated core excitation.
U.S. Pat. No. 4,274,052 utilizes a single winding on each core wherein each winding is sinewave voltage excited for core saturation. Circuitry is shown for the detection of the second harmonic of the excitation frequency. A manual adjustment is also utilized to provide the feedback necessary to null the effects of the unknown current.
U.S. Pat. No. 4,276,510 illustrates a measuring device in which separate excitation and feedback windings are used along with a phase detection method that is implemented using squarewave voltage excitation.
U.S. Pat. No. 4,278,938 illustrates a current measuring device in which a plurality of windings are used on a single core for excitation and feedback. A voltage pulse excitation method is used to detect the value of the unknown current.
Canadian Pat. No. 763,576 illustrates an electrical current measuring apparatus which utilizes a pair of cores and three windings. By utilizing voltage excitation, the cores are excited into saturation and the second harmonic of excitation frequency is detected.
Japanese Pat. No. 54-97730 illustrates a current detection circuit utilizing two windings plus a split-gap flux detector to perform the DC current measurement.